Solenoids are typically classified as any electromagnetic device that converts electrical energy to linear momentum. Solenoids may include a coil conductor wrapped around a metallic piston that serves as an armature. When voltage is applied to the coil terminals, current is passed through the coil conductor generating an electromagnetic field, which draws the metallic piston toward the field. An electronic controller may be coupled to the solenoid for regulating the flow of current through the coil conductor to control the electromagnetic field.
Position of the piston may be manipulated by controlling the strength of the electromagnetic field. For example, in order to initially actuate the solenoid armature, voltage may be applied across the coil conductor, energizing the coil and strengthening the electromagnetic field associated with the coil. When the electromagnetic force becomes strong enough to overcome the static kinetic forces associated with the armature, the armature is “pulled-in” toward the field. Once the armature has moved to the “pulled-in” position, current in the coil may be reduced to a minimum level required to hold the armature in place (i.e., “hold-in” current). To release the armature, thereby allowing its return to original (i.e., “rested”) state, the current through the coil conductor may be cut-off, allowing the electromagnetic field to dissipate. Once the current level in the coil falls below the “hold-in” current, the electromagnetic forces acting on the armature are no longer sufficient to hold the armature in place, and the armature is returned to its rested state.
In certain situations, it may be beneficial to know when the armature is actuated. For example, in electronic fuel injection systems for combustion engines, fuel-efficient operation of the engine may depend on the precise operation of one or more solenoid valves. Effective determination of the operation of the solenoid valves may depend not only on the time in which the control signals are sent to the solenoid, but on the actuation time of solenoid armatures that may open and close the valves. Thus, a system and method for accurately determining armature movement time may be required.
At least one system has been developed to detect a “drop-off” condition associated with a magnetically operated device. For example, U.S. Pat. No. 6,188,562 (“the '562 patent”), which was issued to Lutz et al. on Feb. 13, 2001, describes a method and apparatus for recognizing an accidental closure of a solenoid valve. The system of the '562 patent is configured to monitor the frequency of a pulsed hold-in current and determine, based on an increase in the frequency, that an armature associated with the solenoid valve has accidentally dropped off, causing the valve to erroneously close.
Although the system of the '562 patent may determine an erroneous or accidental drop-off of a solenoid armature, it may be problematic. For example, because the system may only monitor the frequency of the pulsed signal that supplies the hold-in current to detect accidental drop-off, it may not determine when the actuator returns to its original position after the hold-in current has been turned off. As a result, systems requiring accurate detection of armature movement under normal operating conditions may become inefficient and inaccurate.
The presently disclosed systems and methods for detecting solenoid armature movement are directed to overcoming one or more of the problems set forth above.